v0.2.0 — schema, validator, and the full upgrade path

The kit's first post-launch release. Highlights: a documented artifact schema (templates/README.md) with a stdlib validator (scripts/validate.py); the missing aspirational.md template; machine-readable schemas/ shared with the hosted app; per-tier overdue nudges; a safe privacy-mode switcher; MIT LICENSE in-tree; module READMEs; a fully worked fictional example corpus covering every artifact type; and the CHANGELOG/UPGRADING flow for pulling structure updates into a fork. Breaking (see CHANGELOG 0.2.0): the id: frontmatter field is gone (the filename is the id) and goal's met_on: is now the uniform ended_on:.